I’m cruising a tropical lagoon on the trail of an underwater lawnmower. Elan Cuevas, my boatman and guide, is at the wheel, manoeuvring behind a telltale slick of grass clippings. He squints against the surface glitter of sunlight. Follow the trail, he knows, and we might get lucky.

The lagoon in question is Placencia, on the south coast of Belize, and the lawnmower is a West Indian manatee. This endearing sea cow finds sanctuary here, courtesy of an extensive No Wake zone that prevents collisions with power boats – a major threat. But finding one takes a bit of work.

“Over there,” says Elan. “See the mud?” He points to a gravy-stain bloom of sediment at the surface, betraying a manatee busy...